Method for adding tellurium to steel



Jan. 11, 1966 c. F. SCHRADER ETAL 3,

METHOD FOR ADDING TELLURIUM TO STEEL Filed Feb. 1. 1965 United States Patent 3,228,766 METHOD FUR ADDING TELLURIUM T0 STEEL Carlton B. Schratler, Chesterton, and Kurt R. Mattson, Crown Point, lnd., assignors to Inland Steel Company, (Ihicago, lll., a corporation of Delaware Filed Feb. l, 1965, Ser. No. 429,282 6 Claims. (Cl. 75129) This is a continuation-in-part of application Serial No. 191,477 filed May 1, 1962, and now abandoned.

The present invention relates generally to methods for adding ingredients to molten steel in a ladle, and more particularly to methods for adding tellurium, either alone or together with certain other ingredients.

The addition of tellurium to molten steel increases the machinability of the ultimate solidified steel product. Typical examples of steels having increased machinability due to the addition of tellurium are described in Holo- Waty U.S. Patent Number 3,152,889.

When tellurium is exposed to the atmosphere at the temperature of molten steel, the tellurium will oxidize and/or vaporize, causing substantial amounts of fuming and a relatively low recovery of the tellurium. Because tellurium is extremely expensive compared to the cost of other ingredients added to steel, it is important that the tellurium be added to steel under conditions which provide maximum recovery of the tellurium while at the same time obtaining optimum distribution.

In accordance with the present invention, these goals can be accomplished by adding tellurium to the steel in a ladle in a manner whereby the tellurium is covered and protected from the atmosphere by the molten steel both quickly and quietly after initial contact with the steel.

More specifically, when tellurium is added to steel in the ladle, it should be placed on the bottom of an empty ladle, before the molten steel is introduced thereinto, and concentrated at a position in which the tellurium is not subjected to the downward impact of the descending stream of molten steel and, additionally, where the turbulence and swirling about of the molten metal accumulating in the ladle is at a minimum. Such a position is one where the flow velocity of the molten steel along the ladle bottom is at a minimum. With round ladles generally utilized in the steel-making industry, the position best suited to these objectives will be at the periphery of the ladle bottom diametrically opposite and furthest from the point of impact of the molten steel stream which is directed toward the bottom or side of the ladle at the periphery thereof. It is possible that this position may vary from the peripheral position described above depending upon the size or shape of the ladle, which may approach a rectangular shape rather than being substantially round, and also with differences in the directional characteristics of the stream due to different relationships from steel-making plant to steel-making plant between the ladle and the tapping lip which communicates with the ladle. However, for any given ladle, so long as all the tellurium is concentrated at a location on the ladle bottom where the flow velocity of the molten steel along the ladle bottom is a minimum, recovery of the tellurium will be at a maximum.

If sulphur is also to be added to the steel, said sulphur normally being placed on the bottom of the ladle before the molten steel is introduced thereinto, it is important that the sulphur be positioned so as to obtain as long an interval as is practically possible between the time the molten steel contacts and reacts with the sulphur and the time the molten steel contacts the tellurium. This is because when sulphur is contacted by molten steel, a substantial portion of the sulphur burns, generating a large amount of heat and causing a substantial amount of turbulence. Under these conditions, if the tellurium were contacted by the molten steel before the effects of the sulphur-molten steel reaction had been substantially manitested, there would be unduly large oxidation of and fuming by the tellurium, and recovery would be low.

In the above described method for adding tellurium to steel it is also important that ladle additions, other than sulphur, be applied in forms other than their specially prepared strongly exothermic forms, now quite commonly used as ladle additions in steelmaking. This is because strongly exothermic ladle additions create intense heat and agitation resulting in substantially lower recovery of tellurium. Illustrative of these strongly exothermic materials are chrome and manganese ferro-alloys containing strong oxidizing and reducing agents such as aluminum or silicon and sodium nitrate. A ladle addition which is not exothermic is one which is endothermic or possibly one which is neither exothermic nor endothermic.

Tellurium may be added to molten steel in any of several solid forms, including pigs, pellets, sticks, slugs, etc. A typical tellurium addition constitutes about 1.4 lbs. per ton of steel for a ladle addition.

Conventionally, ladles are preheated before molten steel or addition ingredients are introduced therein. Accordingly, when an amount of tellurium in small divided form, such as pellets, is concentrated at a location on the bottom of the preheated ladle, the heat of the ladle raises the temperature of the tellurium and the individual pellets become tacky and stick together forming a mass or agglomerate which is not likely to be dispersed into small segments after being contacted by the molten steel. By the time there is suflicient molten steel in the ladle to buoy the tellurium mass and urge it toward the top of the bath where undesired oxidation of the tellurium can occur, the tellurium mass will have been enveloped by and substantially melted into the molten steel, thus minimizing the problem of oxidation which could otherwise arise when tellurium in small, divided form is used.

Other features and advantages are inherent in the methods claimed and described, or will become apparent to those skilled in the art from the following detailed description in conjunction with the accompanying diagrammatic drawings, wherein:

FIGURE 1 is a plan view of an empty ladle containing additions of tellurium and sulphur; and

FIGURE 2 is a side elevational view of the ladle of FIGURE 1.

Referring to the figures, the numeral 10 indicates an empty ladle having a round cross-section, into which a stream of molten steel is to be introduced by a runner 13 from a furnace (not shown). The runner is disposed, relative to ladle 10, so that the stream of steel follows the path indicated by the dotted line 14 from runner 13 to ladle it Placed on the bottom of ladle 10 at the periphery thereof is an addition of tellurium 11. In the embodiment illustrated in the figures the peripheral location of the tellurium is the one which is removed the maximum possible distance from the place of impact of the stream of molten steel and one Where the turbulence and flow velocity of the molten steel along the ladle bottom is at a minimum. The molten steel hits the ladle bottom or side at a position diametrically opposite from the tellurium, and flows from the location of impact to the location of the tellurium. As the stream of molten steel flows across the bottom of the ladle, its fiow velocity decreases, and by the time the stream covers the distance from the location of impact to the tellurium, its velocity is minimized. Instead of violently striking the tellurium, the molten steel gradually envelopes the tellurium as the molten steel level rises in the ladle.

f the tellurium were positioned in some location other than that described above (i.e., nearer the location of impact of the stream of steel entering the ladle) the tellurium would be contacted by a stream of steel having a relatively high velocity compared to the velocity of the steel stream when it contacts the tellurium located as in FIGURES 1 and 2. The impact of the turbulent or relatively high velocity molten stream would subject the tellurium to a substantial amount of agitation. This agitation would cause at least some of the tellurium to separate from the concentrated mass and rise to the surface of the molten steel in the ladle, whereupon this tellurium would react with the atmosphere or with ladle scum on top of the molten steel, thereby substantially reducing the recovery of the tellurium. Thus, in accordance with the present invention all the tellurium is concentrated at a position where the flow velocity of the molten steel along the ladle bottom is at minimum. The area of ladle bottom covered by the tellurium concentration is relatively small compared to the area not covered by tellurium.

In the above-described embodiment, the ladle It is wide enough at its bottom so that the tellurium at 11 is not aflFected by splashes from the molten steel striking the ladle bottom at a location diametrically opposite the tellurium at 11.

In situations where the ladle bottom is so narrow that tellurium situated at 11 on the ladle bottoms periphery would be subjected to splashing by a substantial portion of the molten steel having a location of initial impact 12 at a diametrically opposite location from the tellurium, the location of the tellurium would have to be changed from that indicated at 11 in the figures. However, the location of the tellurium would still be one where the flow velocity of the molten steel along the ladle bottom is a minimum in accordance with the method of the present invention.

Thus, in a situation Where the location of initial impact of molten steel entering a ladle is at the periphery of the ladle bottom, and the location of rebound impact of the stream of molten steel is at or close to the diametrically opposite location on the ladle bottom, the tellurium may be concentrated on the ladle bottom at a location spaced from both the location of initial impact and the location of rebound impact of the molten steel and at which location the flow velocity of the molten steel is a minimum. conceivably, under certain special circumstances, this could be closer to the location of initial molten steel impact than to a location diametrically opposite the location of initial impact.

It sulphur, or an ingredient reacting like sulphur at the temperature of molten steel, is to be added to the steel in the ladle, it should be positioned so that the interval between the time the molten steel contacts and reacts with the sulphur and the time the molten steel contacts the tellurium is a maximum. Thus, in the figures, the sulphur addition 12 is located at the place of impact of the molten steel and the tellurium is diametrically opposite the sulphur, both being located at the periphery of the ladle.

If the tellurium were to be positioned elsewhere, closer to the sulphur or like ingredient, the heat and turbulence generated by the reaction of the sulphur or equivalent ingredient would cause substantial burning or oxidation and fuming of the tellurium.

Exothermic ferroalloys, when added to molten steel, generate so much heat and turbulence that even if the interval between molten steel-exothermic ferroalloy contact and molten-steel tellurium contact is a maximum, there will be a substantial adverse effect on the recovery of the tellurium. Accordingly, strongly exothermic ferroalloys should not be added to molten steel in the ladle to which tellurium is being added, and ladle additions should be either endothermic or neither exothermic nor endothermic.

When tellurium is added to the ladle, the recovery is slightly lower than if the tellurium were added to the ingot mold, about 61% to 73%. However, the uniformity of tellurium content from ingot to ingot is greater if the tellurium is added in the ladle.

There have thus been described methods for adding tellurium to steel, either alone or together with other ingredients, and utilizing techniques which provide maximum recovery of the tellurium. The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

Although the subject method has been described herein with respect to tellurium, the method is equally applicable for the addition to molten steel of other ingredients having reaction characteristics like those of tellurium. For example, to assure maximum recovery and optimum distribution of selenium, the addition thereof should be made in accordance with the subject method.

What is claimed is:

1. A method for making a ladle addition to steel of a component constituting at least one element selected from the group consisting of selenium and tellurium, said method comprising the steps of:

placing all of said component, in solid form, on the bottom of a ladle, before any molten steel is introduced therein; said placing step including concentrating all of said component at a location which covers no more than a portion of the area of the ladle bottom;

the area of ladle bottom covered by said component being relatively small compared to the area of ladle bottom not covered by said component;

and introducing a stream of molten steel onto the bottom of said ladle at the periphery of said ladle bottom and flowing the molten steel along the bottom of the ladle from a location of molten steel impact on the ladle bottom remote from said components location;

said components location constituting the location on the ladle bottom where the flow velocity of the molten steel along the ladle bottom is at a minimum.

2. A method as recited in claim 1 and comprising adding to said ladle a ferroalloy consisting of an endothermic ferroalloy.

3. A method as recited in claim 1 wherein said component is concentrated at a location on the periphery of the ladle bottom which is diametrically opposite the location of initial impact of molten steel introduced into the ladle.

4. A method as recited in claim 3 and comprising:

introducing sulphur into the steel by placing said sul phur, in solid form, in the ladle before said molten steel is introduced into the ladle and at the location of initial impact of the molten steel. 5. A method for making ladle additions to steel of sulphur and another component constituting at least one element selected from the group consisting of selenium and tellurium, said method comprising:

placing all of said sulphur, in solid form, at a location on the bottom of the ladle at the periphery thereof before any molten metal is introduced therein;

placing all of said other component, in solid form, on the bottom of said ladle, before any molten metal is introduced therein, at a location spaced from the location of said sulphur; 2

introducing a stream of molten steel onto the ladle bottom at the periphery thereof;

the location of impact of said stream of molten steel on the ladle bottom being the location of said sulphur;

said other component having a location and a distribution for which the interval between the time when molten steel contacts and reacts with said sulphur 5 and the time when the molten steel contacts the 2,236,716 other component is substantially a maximum; 2,250,488 and then pouring said molten steel from the ladle. 2,258,604 6. A method as recited in claim 5 wherein said sul- 2,364,922 phur and said other component are placed in diametrically 5 2,595,292 opposite locations on the bottom of the ladle. 2,661,279

References Cited by the Examiner UNITED STATES PATENTS Morris 72123 Lorig et a1. 75 Gabnebin 75--58 Smalley 75-130 Reece 75-429 Wilcox et a1. 7558 OTHER REFERENCES Waterhouse and Zaverine: Iron Age, Dec. 13, 1923,

DAVID L. RECK, Primary Examiner. 

1. A METHOD FOR MAKING A LADLE ADDITION TO STEEL OF A COMPONENT CONSTITUTING AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF SELENIUM AND TELLURIUM, SAID METHOD COMPRISING THE STEPS OF: PLACING ALL OF SAID COMPONENT, IN SOLID FORM, ON THE BOTTOM OF A LADLE, BEFORE ANY MOLTEN STEEL IS INTRODUCED THEREIN; SAID PLACING STEP INCLUDING CONCENTRATING ALL OF SAID COMPONENT AT A LOCATION WHICH COVERS NO MORE THAN A PORTION OF THE AREA OF THE LADLE BOTTOM; THE AREA OF LADLE BOTTOM COVERED BY SAID COMPONENT BEING RELATIVELY SMALL COMPARED TO THE AREA OF LADLE BOTTOM NOT COVERED BY SAID COMPONENT; 